In the storage and retrieval of information, digital tape recording and reproducing apparatus has been employed. Such apparatus of more recent vintage includes a scanner assembly, in which the scanner spindle must be relatively free of radial movement to ensure that the scanning heads traverse a predictable and repeatable path. Such scanning heads operate at normal rotational speeds in excess of 5,400 revolutions per minute and, during variable play or search operation, may run at speeds up to 9,000 RPM. With track widths in such digital tape machines presently in the 20 to 40 micron range, it is imperative that the spindle assembly maintain a consistent and unchanging positional relationship to the tape guiding reference features of the tape drive. Axial compliance between the bearing pair is required to allow for differential thermal expansion between the shaft or spindle and housing. Radial play must be eliminated, for this will translate into a change in the scan plane relative to the remainder of the tape drive.
In prior art spindle assemblies, spring pre-loaded spindle assemblies have been employed. One such unit, generally designated 110, is shown in FIGS. 1A and 1B, in which a rotatable shaft 112 has first and second reduced diameter ends 112a and 112b thereof supported by the fixed attachment to the inner races 114a and 116a of ball bearing assemblies, generally designated 114 and 116, the inner races being secured to the shaft 112 by suitable means such as nut members 127 and 128. The outer races 114b and 116b of the bearing assemblies 114 and 116 are suitably supported within a housing or other support member, generally designated 118, which includes a central tubular opening 119 through which the shaft 112 extends in concentric relation therewith. The outer race 114b of bearing assembly 114 is securely mounted within an enlarged opening 121 configured for securely receiving therein the outer race 114b, which is fixed within the enlarged diameter opening 119 by adhesive or by a press fit. The other end of the tubular opening 119 is provided with a second enlarged diameter opening 123 having a greater depth than the opposite opening 121. Assembled within the opening 123 is a compression pre-load spring 125, the outer diameter of which approximates the inner diameter of the opening 123. One end of spring 125 rests against the shoulder 123a of opening 123, while the other end urges against the inner surface of the outer race 116b of bearing 116. The outer race 116b is loosely retained within the opening 123, that is, the inner diameter of opening 123 is slightly greater than the outer diameter of outer race 116b, providing a radial gap which is required to allow axial compliance for pre-load control. The shaft ends 112a and 112b have a diameter sufficient to receive thereon the openings of the inner races 114a and 116a of bearings 114 and 116, respectively. As can be seen by viewing the ball bearings 114c and 116c of the bearings 114 and 116, the effect of the pre-loading is to urge the outer races 114b and 116b away from one another, that is the dimension between the inner surfaces of inner races 114a and 114b is less than the dimension between the opposing inner surfaces of outer races 114b and 116b. This effect causes the bearing positions to be closer to the outer edges of the inner bearing races 114a and 116a, and correspondingly, closer to the inner edges of the outer bearing races 114b and 116b. Such pre-loading of spindle assemblies has been done in an attempt to eliminate axial motion of the spindle at the fixed bearing 114 while still allowing for differential thermal expansion between the housing and shaft by extension or compression of the pre-load spring 125 and slight relative motion between the housing 118 and the "floating bearing" 116.
As shown in FIG. 1A, the outer diameter of outer race 116b of bearing 116 is concentric with the opening 123. However, upon rotation, and especially under load, there is a bearing radial shift of bearing 116, that is, the bearing which coacts with the pre-load compression spring 123. This effect is undesirable and results in loss of axis control since any radial shift will cause an angular displacement of the axis of the shaft 112 relative to the housing mount or support member 118, this angular displacement being represented by the distance between the two broken axial lines having an angular displacement distance "X" therebetween.
In accordance with an aspect of the present invention, there is provided an axially displaced flexural bearing support assembly including a unitary or monolithic bearing support base member having a bearing receiving tube supported by first and second generally parallel flexural spoke members which allows both outer races to be fixed by adhesive or press fit to their respective bearing bores, thus eliminating the radial clearance while the flexural spring characteristics of the spoke members allow sufficient axial compliance to prevent bearing overload due to thermal differential expansions.
The present invention obviates many of the disadvantages of the prior art and provides further related advantages.